Morphological Characteristics of Ephemeral Stream Channel and Overbank Splay Sandstone Bodies in the Permian Lower Beaufort Group, Karoo Basin, South Africa

  1. J. D. Collinson and
  2. J. Lewin
  1. Willo M. Stear

Published Online: 29 APR 2009

DOI: 10.1002/9781444303773.ch33

Modern and Ancient Fluvial Systems

Modern and Ancient Fluvial Systems

How to Cite

Stear, W. M. (1983) Morphological Characteristics of Ephemeral Stream Channel and Overbank Splay Sandstone Bodies in the Permian Lower Beaufort Group, Karoo Basin, South Africa, in Modern and Ancient Fluvial Systems (eds J. D. Collinson and J. Lewin), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303773.ch33

Author Information

  1. Rand Mines Ltd, P.O. Box 62370, Marshalltown 2107, South Africa

Publication History

  1. Published Online: 29 APR 2009
  2. Published Print: 7 FEB 1983

ISBN Information

Print ISBN: 9780632009978

Online ISBN: 9781444303773

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Keywords:

  • morphological characteristics of ephemeral stream channel and overbank splay sandstone bodies – Permian Lower Beaufort Group, Karoo Basin, South Africa;
  • high flow regime bedforms;
  • periodic stage fluctuations;
  • stratigraphic mapping;
  • taphonomy

Summary

Fining-upward cyclic sequences in the lower part of the Beaufort Group of Permian age represent the deposits of an ancient ephemeral stream–playa lake complex analogous with some of those forming in modern semi-arid inland basins. Sheet-like and lenticular sandstone bodies occur as superimposed systems of fluvial channels and overbank splays formed by multiple lateral and vertical accretion. Excellent outcrop conditions provide sufficient transverse cross-sectional exposures of numerous palaeochannels to permit a general two-fold morphological subdivision of the sandstone bodies into sheet and ribbon types. Most of the channel sandstone bodies have a multi-storey composition and many display prominent sets of ‘wings’ which taper away from the channel-fill deposits as thinner overbank sandstone sheets.

The bulk of the channel-fill deposits consists of high flow regime bedforms and most of the palaeochannels contain features indicative of periodic stage fluctuations. Well-preserved sandstone palaeosurfaces in channel and splay sequences contain a wide variety of sedimentary structures that are attributable to fluctuating hydrodynamic conditions in the falling water stages of floods and during subaerial emergence.

The morphology and internal geometry of the sandstone bodies are adopted as prime criteria for determining the original channel patterns and flow characteristics of the river systems.

The ephemeral streams of the Lower Beaufort were typified by channel patterns that were both straight and highly sinuous and probably displayed various transitions between these two types along their drainage courses.